Rotation detecting device having a terminal holding arrangement

ABSTRACT

A rotation detecting device comprising a pole formed of a ferromagnetic material, a bias magnet for applying a magnetic flux to the pole, a bobbin receiving the pole and the bias magnet in a series arrangement, a detecting coil mounted on the bobbin, terminals each having a coil connecting part connected to one end of the wire of the coil and a lead wire connecting part connected to a lead wire, a cap for covering the terminals and a portion of the bobbin holding the terminals, fixing means for fixing the terminals to the bobbin.

This is a division of application Ser. No. 201,856 filed on June 3,1988, now U.S. Pat. No. 4,888,551.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rotation detecting device fordetecting the angular displacement of a magnetic body and capable ofimproving the reliability of finishing the ends of a detecting coil.

2. Discussion of Background

The conventional magnetic rotation detecting device has a magneticcircuit comprising (1) a pole, (2) a bias magnet and (3) a detectingcoil.

A high output voltage of the detecting coil can be obtained by meanssuch as (a) providing a fixed pole having a high magnetic permeability,(b) providing a bias magnet having a high magnetic flux density or (c)increasing the number of turns of the detecting coil. Generally, themeans (c) is employed to obtain a high output voltage of the detectingcoil.

However, a very thin wire must inevitably be used for forming thedetecting coil to increase the number of turns within a limited spaceand ordinarily a wire of 0.13 mm to 0.15 mm in diameter is used forforming such a detecting coil. The ends of the wire are connected toterminals for lead wires, for example, by soldering. If the junctions ofthe ends of the wire and the terminal is stressed locally, the coil maypossibly be disconnected from the terminal or terminals.

Referring to FIGS. 5, 6(A) and 6(B) showing a conventional rotationdetecting device, there are shown a pole 1 formed of a ferromagneticmaterial, a bias magnet 2 for applying a magnetic flux to the pole 1, aspacer 3 for enhancing the effective magnetic flux of the bias magnet 2,a bobbin 4 receiving the pole 1 therein, a detecting coil 5 wound on thebobbin 4, the ends 5a of a wire forming the detecting coil 5, which arerespectively wound around the connecting sections 6a of terminals 6provided on the bobbin 4, and lead wires 7 respectively connected to thelead connecting sections 6b of the terminals 6.

Projections 4a and 4b are provided respectively at predeterminedpositions on the outer circumference of the bobbin 4. The projection 4ais engaged with a cap 8, and the terminals 6 are fitted respectively onthe projection 4b. The pole 1, the bias magnet 2 and the spacer 3 arefixed in place by the cap 8. The lead wires 7 are connected respectivelyto the terminals 6 by putting the cap 8 on the projection 4a. The bobbin4 mounted with the detecting coil 5 is received in a housing 10 formedof a plastic material such as Nylon by injection molding. The housing 10is attached to a transmission case or the like with a screw so that therotation detecting device is disposed near a rotary member. The housing10 has a cylindrical fitting part 10a, a reduced part 10b having adiameter smaller than that of the fitting part 10a, an annular groove10c for receiving an O-ring 11 therein, and a supporting part 10d. Alocking bush 12 is provided in the supporting part 10d of the housing 10to prevent the screw fastening the housing 10 to a transmission case orthe like from loosening.

When the rotation detecting device is mounted on the transmission case,the pole 1 is located near a projection provided on the rotary member.When the projection of the rotary member approaches the pole 1 as therotary member rotates, the magnetic lines of force of the bias magnet 2extend from the bias magnet 2 through the pole 1, the rotary member, theexternal space and the spacer 3 to the bias magnet 2. Since the magneticlines of force extend across the coil 5, voltage is induced in thedetecting coil 5 as the magnetic flux varies according to the variationof the distance between the projection of the rotary member and thepole 1. The rotating speed of the rotary member is calculated by usingthe induced voltage. Such an induced voltage induced in the coil of therotation detecting device is used also for detecting the approach of anobject.

In assembling this conventional rotation detecting device, theconnection of the lead wires 7 and the terminals 6 and the connection ofthe ends 5a of the wire of the coil 5 and the terminals 6 areimplemented in the following procedure.

(1) The lead wires 7 are fixedly connected to the lead wire connectingparts of the terminals 6 by crimping.

(2) The ends of the wires of the detecting coil 5 are wound severalturns respectively around the U-shaped coil connecting parts 6a of theterminals 6, and then the ends of the wires of the detecting coil 5 arefixed to the coil connecting parts 6a by soldering.

(3) The lead wire connecting parts 6b of the terminals 6 are placedbetween the projections 4a and 4b of the bobbin 4.

(4) The cap 8 is put on the housing 10 so as to cover the terminals 6,the rear part of the bobbin 4 and the extremities of the lead wires 7.

When the rotation detecting device is thus assembled, a clearance Δx inthe range of 0.2 mm to 0.3 mm is formed between the rear end of the leadwire connected parts 6b of the terminals 6 and the projection 4a of thebobbin 4, and hence the terminals 6 are movable to the left, as viewedin FIG. 6(B), by a distance Δx when the lead wires 7 are pulled to theleft. Therefore, the wire of the coil 5 maay possibly be broken when thelead wires 7 are pulled to the left if the slack of the wire between thecoil 5 and the coil connecting parts 6a of the terminals 6 is smallerthan the clearance Δx. Such a trouble occurs before injection moldingand will not occur after injection molding because the terminals 6 arefixed by the molding and the ends 5a of the wire of the coil 5 will notbe pulled even if the lead wires 7 are pulled.

However, in placing the assembly of the bobbin 4, the coil 5, theterminals 6 and the lead wires 7 in a mold for injection molding, thelead wires 7, in general, are pulled to set the assembly accurately inthe mold, which often causes the breakage of the ends 5a of the wire ofthe coil 5.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide arotation detecting device constructed so that no force acts on the endsof the wire of the coil even if the lead wires are stressed by anexternal force such as tension, capable of preventing the breakage ofthe wire of the coil, and having remarkably improved reliability.

To achieve the object of the invention, the present invention provides arotation detecting device comprising a pole formed of a ferromagneticmaterial, a bias magnet for applying a magnetic flux to the pole, abobbin receiving the pole and the bias magnet in a series arrangement, adetecting coil mounted on the bobbin, terminals each having a coilconnecting part connected to one end of the wire of the coil and a leadwire connecting part connected to a lead wire, a cap for covering theterminals and a portion of the bobbin holding the terminals, fixingmeans for fixing the terminals to the bobbin.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from the following description taken inconjunction with the accompanying drawings, in which:

FIG. 1(A) is an enlarged fragmentary plan view of a rotation detectingdevice, in a first embodiment, according to the present invention,showing a terminal and a bobbin;

FIG. 1(B) is an enlarged fragmentary longitudinal sectional view of therotation detecting device, corresponding to FIG. 1(A);

FIG. 2(A) is an enlarged fragmentary plan view, similar to FIG. 1(A), ofa rotation detecting device, in a second embodiment, according to thepresent invention, showing a terminal and a bobbin;

FIG. 2(B) is an enlarged fragmentary longitudinal sectional view of therotation detecting device of FIG. 2(A);

FIG. 3(A) is an enlarged fragmentary plan view, similar to FIG. 1(A), ofa rotation detecting device, in a third embodiment, according to thepresent invention, showing a terminal and a bobbin;

FIG. 3(B) is an enlarged fragmentary longitudinal view of the rotationdetecting device of FIG. 3(A);

FIG. 4 is an enlarged fragmentary perspective view of part of the bobbinemployed in the third embodiment;

FIG. 5 is a longitudinal sectional view of a conventional rotationdetecting device;

FIG. 6(A) is an enlarged fragmentary plan view of the conventionalrotation detecting device of FIG. 5, showing a terminal and a bobbin;and

FIG. 6(B) is an enlarged fragmentary longitudinal sectional view of therotation detecting device of FIG. 6(A).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description of the preferred embodiments of the presentinvention, parts similar to those previously described with reference toFIGS. 5, 6(A) and 6(B) showing the conventional rotation detectingdevice will be denoted by like reference numerals and the descriptionthereof will be omitted. Only the features of the present invention willbe described hereunder.

Referring to FIGS. 1(A) and 1(B), a rotation detecting device comprisesa bobbin 4, terminals 6, a cap 8, and other components which are similarto those of the conventional rotation detecting device. A positioninghole 6c is formed in the upper surface, as viewed in FIG. 1(A), namely,in the surface opposite the lead wire holding surface, of a terminal 6.

A positioning projection 4c is formed in a bobbin 4 at a positioncorresponding to the positioning hole 6c of each of the terminals 6 onthe bobbin 4 when the terminals 6 are mounted on the bobbin 4 at correctpositions. The positioning projections 4c may be formed integrally withthe bobbin 4 or may be separate members attached to the bobbin 4.

In assembling the rotation detecting device, the terminals 6 are mountedon the bobbin 4 so that the positioning projections 4c of the bobbin 4engage the positioning holes 6c of the terminals 6, respectively, andthen a cap 8 is pressed against the bobbin 4 to receive the assembly ofthe bobbin 4 and the terminals 6 therein. Since the positioningprojections 4c of the bobbin 4 engage the positioning holes 6c of theterminals 6, the terminals 6 are held fixedly on the bobbin 4 and areunable to move relative to the bobbin 4 even if there is a clearance Δxbetween the rear end of the terminals 6 and projections 4a formed in thebobbin 4 and even if an external force is applied to lead wires 7connected to the terminals 6 after assembly, and thereby the accidentalbreakage of the wires of the detection coil 5 is prevented to enhancethe reliability of the rotation detecting device.

Referring to FIGS. 2(A) and 2(B), a rotation detecting device comprisesa bobbin 4, terminals 6, a cap 8, and other components which are similarto those of the conventional rotation detecting device. A sawtooth ridge6d having an upright rear end surface is formed in the central part ofthe upper surface, as viewed in FIG. 2(B) of the lead wire holding part6b of each terminal 6 so as to extend along the axis of the bobbin 4.Axial grooves 8a respectively for receiving the sawtooth ridges 6d ofthe terminals 6 are formed in the inner circumference of the cap 8. Whenthe cap 8 is put in place on the bobbin 4, the upright rear end surfacesof the sawtooth ridges 6d are in contact respectively with the end wallsof the axial grooves 8a of the cap 8.

In assembling the rotation detecting device, the terminals 6 are mountedon the bobbin 4 between projections 4a and 4b of the bobbin 4, and thenthe assembly of the bobbin 4 and the terminals 6 are pushed into the cap8 as deep as the upright rear end surfaces of the sawtooth ridges 6d ofthe terminals 6 come into contact respectively with the end surfaces ofthe axial grooves 8a, and thereby the terminals 6 are held fixedlybetween the bobbin 4 and the cap 8.

Thus, the second embodiment is the same in effect as the firstembodiment.

Referring to FIGS. 3(A), 3(B) and 4, a rotation detecting devicecomprises a bobbin 4, terminals 6, a cap 8, and other components whichare similar to those of the conventional rotation detecting device. Thebobbin 4 has two pairs of projections 4a and 4d capable of beingdeformed easily by a small pressure and formed integrally therewith atthe rear end, namely, at the left end as viewed in FIG. 3(B), thereof.In each pair of projections, 4a and 4d are separated from each other bya predetermined distance to form a U-shaped groove 4e therebetween asbest shown in FIG. 4. A lead wire 7 is extended through the U-shapedgroove 4e and is held between the pair of projections 4a and 4d.

In assembling the rotation detecting device, the terminals 6 are put inplace on the bobbin 4 between the pairs of projections 4a and 4d, andprojections 4b, respectively. Then, the assembly of the bobbin 4 and theterminals 6 is pushed into the cap 8 as far as the rear end of thebobbin 4 comes into contact with the inner bottom surface of the cap 8.As the assembly of the bobbin 4 and the terminals 6 is pushed into thecap 8, the pairs of projections 4a and 4d are bent toward the front end,namely, the right end as viewed in FIG. 3(B), of the bobbin 4 to pressthe terminals 6 respectively against the projections 4b of the bobbin 4,and thereby the terminals 6 are held firmly respectively between thepairs of the projections 4a and 4d, and the projections 4b.

The third embodiment is the same in effect as the first embodiment.

Although the invention has been described with reference to preferredforms thereof with a certain degree of particularity, obviously manychanges and variations are possible therein. It is therefore to beunderstood the present invention may be practiced otherwise thanspecifically described herein without departing from the scope andspirit thereof.

What is claimed is:
 1. A rotation detecting device comprising:a poleformed of a ferromagnetic material; a bias magnet for applying amagnetic flux to the pole; a bobbin receiving the pole and the biasmagnet in a series arrangement; a detecting coil mounted on the bobbin;a pair of terminals each having a coil connecting part connected to aseparate end of the wire of the coil and a lead wire connecting partconnected to a separate lead wire, said terminals being received withinsaid bobbin; a cap which fits around said bobbin for covering theterminals and a portion of the bobbin holding the terminals; fixingmeans for fixing the terminals to the bobbin, the fixing means beingsawtooth ridges formed respectively in the outer surfaces of theterminals, and grooves formed in the cap, capable of receiving thesawtooth ridges therein, respectively, the respective end surfaces ofthe grooves engaging the upright end surfaces of the sawtooth ridges,respectively, when the cap is put on the assembly of the bobbin and theterminals.
 2. A rotation detecting device comprising:a pole formed of aferromagnetic material; a bias magnet for applying a magnetic flux tothe pole; a bobbin receiving the pole and the bias magnet in a seriesarrangement; a detecting coil mounted on the bobbin; a pair of terminalseach having a coil connecting part connected to a separate end of thewire of the coil and a lead wire connecting part connected to a separatelead wire, said terminals being received within said bobbin; a cap whichfits around said bobbin for covering the terminals and a portion of thebobbin holding the terminals; fixing means for fixing the terminals tothe bobbin, the fixing means being a plurality of pairs of deformableprojections formed in the bobbin, the deformable projections of eachpair being spaced apart from each other by a predetermined distance soas to define a U-shaped groove therebetween, the pairs of deformableprojections being deformed so as to hold the lead wires firmlytherebetween when the cap is put on the bobbin.